1. Field of the Invention
The present invention relates to a grain-oriented electrical steel sheet and a process for the preparation thereof. More particularly, the present invention relates to a technique of providing a high-flux density, grain-oriented electrical steel sheet in which the watt loss characteristic is greatly improved by the magnetic domain-controlling treatment of the surface of the steel sheet.
2. Description of the Related Art
A process is known for reducing the watt loss by subjecting the surface of a high-flux density, grain-oriented electrical sheet to an artificial magnetic domain-controlling treatment in a direction substantially orthogonal to the rolling direction. More specifically, Japanese Unexamined Patent Publication No. 55-18566 and Japanese Unexamined Patent Publication No. 58-73724 disclose a process in which the surface of the electrical steel sheet is irradiated with laser beams at predetermined intervals; Japanese Unexamined Patent Publication No. 61-96036 discloses a process in which intrusions are formed at predetermined intervals; Japanese Unexamined Patent Publication No. 61-117218 discloses a process in which grooves are formed at predetermined intervals; Japanese Unexamined Patent Publication No. 61-117284 discloses a process in which a part of the base steel is removed at predetermined intervals and a phosphate-type tension coating is formed on the surface; and Japanese Unexamined Patent Publication No. 62-151511 discloses a process in which the surface of the electrical steel sheet is brought into contact with a plasma flame at predetermined intervals.
By the adoption of the above-mentioned technique of the artificial magnetic domain control, the watt loss characteristic can be considerably improved in a high-flux density, grain-oriented electrical steel sheet, and this technique has met current demands, i.e., to save energy, through a reduction of the watt loss in a transformer constructed by using this steel sheet.
Nevertheless, the requirements for saving energy are increasing, and it has become necessary to further enhance the performance of a grain-oriented electrical steel sheet as the material of a transformer.